Synthesis of mesoporous aluminophosphate (AlPO) and investigation of zirconium incorporation into mesoporous AlPOs

Mesoporous aluminophosphate materials with variable amounts of zirconium have been synthesized at room temperature using a nonionic surfactant tri-block copolymer (PEO(20)PPO(70)PEO(20)) as the structure-directing agent. Powder X-ray diffraction of as-synthesized and calcined AlPO and ZrAlPO mesoporous materials shows a single broad peak near 2theta = 2.5 degrees, indicative of the average pore-pore correlation distance. Electron probe microanalysis shows that the ratio of P/Al in the powders is approximately 0.5, far lower than 1.0 for an ideal aluminophosphate framework. XRD, TEM, and N2 adsorption data indicate that the calcined samples consist of wormlike tubular materials having surface areas >350 m2/g and pores in the mesopore range. Electron spin resonance (ESR) studies of the gamma-irradiated and evacuated ZrAlPO samples show signals due to Zr3+ that increase with Zr content in addition to signals due to framework defects (i.e., V centers) and H atoms. The line shape and g values observed for Zr3+ are best explained as arising from a trivalent zirconium ion situated at the framework tetrahedral sites.     

ON THE SPATIAL CORRELATION BETWEEN THE PROTEIN SURFACE AND THE ELECTRON TRANSFER CYCLE IN BACTERIAL PHOTOSYNTHETIC REACTION CENTERS

Abstract— n -Doxylstearic acids are shown to be electron acceptors in reaction centers from R. spheroides R-26 mutant illuminated with 860 nm light. The electron accepting efficiency varies with n , thus with the location of the nitroxide moiety on the stearic acid chain, and is maximum for 12-doxylstearic acid. In this molecule the nitroxide moiety is 1.4 nm from the polar carboxyl carbon based on molecular models. If the nitroxide moiety is located in or near the polar reaction center protein surface, the results suggest that the quinone-iron complex, which is the ultimate electron acceptor from a bacterio-chlorophyll dimer in the reaction center, is located ∼ 1.4 nm from the protein surface. The protein itself is estimated to have a diameter of 5.4 nm assuming spherical symmetry, so it is postulated that the quinone-iron complex is located on one side of the protein.     

Adaptability at a protein-DNA interface: re-engineering the engrailed homeodomain to recognize an unnatural nucleotide

We explore the adaptability at a protein-DNA interface using phage display to re-engineer a homeodomain to specifically recognize a chemically synthesized, unnatural nucleotide. The engineered homeodomain preferentially binds to the modified DNA with affinity and specificity similar to those of natural homeodomains.     

EPR and eldor studies of CHCl2 in γ-irradiated single crystal dichloromethane

Single crystal dichloromethane grown in quartz tubes was γ-irradiated at 77 K. By studying both CH₂Cl₂ and CD₂Cl₂ with a combination of electron paramagnetic resonance at 9 GHz and 35 GHz together with electron-electron double resonance, it is concluded that the dominant radical formed is ·CHCl₂. Thus in this matrix it appears that dissociative electron capture is not the main net reaction generated by ionizing radiation.     

Coherent soft X-ray magnetic scattering

X-ray sources are exceptional tools for studying the structure of matter down to atomic-length scales, but across a wide range of fields there are samples that have remained notoriously difficult to study, such as airborne particles, particles in solution, membrane proteins, and macromolecular complexes. The advancement of imaging techniques to address these elusive samples has been a big motivation for constructing new X-ray light sources. Fourth-generation light sources, commonly called X-ray free-electron lasers (XFELs) [1 Madey, J. 1971. Journal of Applied Physics, 42: 1906–1913. [Crossref], [Web of Science ®] , [Google Scholar]], represent a huge step forward, with upwards of nine orders of magnitude increase in peak brightness for hard X-rays. As of 2012, four such XFELs are already productively operational (in Germany [2 Ackermann, W. 2007. Nature Photonics, 1: 336–342. [Crossref], [Web of Science ®] , [Google Scholar]], the U.S. [3 Emma, P. 2010. Nature Photonics, 4: 641–647. [Crossref], [Web of Science ®] , [Google Scholar]], Japan [4 Ishikawa, T. 2012. Nature Photonics, 6: 540–544. [Crossref], [Web of Science ®] , [Google Scholar]], and Italy [5 Allaria, E. 2012. Nature Photonics, 6: 699–704. [Crossref], [Web of Science ®] , [Google Scholar]]), with at least five more planned for the next 10 years. These lasers produce femtosecond pulses of extremely intense coherent radiation through the positive feedback between a co-moving electron bunch and the radiation it emits when they traverse an extended undulator. This process creates remarkably strong, tunable probes that will undoubtedly change the way we examine nanoscale structure and dynamics.     

Electrostatic forward-viewing scanning probe for Doppler optical coherence tomography using a dissipative polymer catheter

A novel flexible scanning optical probe is constructed with a finely etched optical fiber strung through a platinum coil in the lumen of a dissipative polymer. The packaged probe is 2.2 mm in diameter with a rigid length of 6mm when using a ball lens or 12 mm when scanning the fiber proximal to a gradient-index (GRIN) lens. Driven by constant high voltage (1-3 kV) at low current (< 5 microA), the probe oscillates to provide wide forward-viewing angle (13 degrees and 33 degrees with ball and GRIN lens designs, respectively) and high-frame-rate (10-140 fps) operation. Motion of the probe tip is observed with a high-speed camera and compared with theory. Optical coherence tomography (OCT) imaging with the probe is demonstrated with a wavelength-swept source laser. Images of an IR card as well as in vivo Doppler OCT images of a tadpole heart are presented. This optomechanical design offers a simple, inexpensive method to obtain a high-frame-rate forward-viewing scanning probe.     

Evidence for the itinerant electron model of ferromagnetism and for surface photoemission from angle-resolved photoemission studies of iron

Angle-resolved HeI photoemission spectra of Fe(001) are reported and interpreted within the framework of a direct transition model using Callaway's ferromagnetic band structure. The generally good agreement between predicted and experimental peak positions is taken to be strong support for the itinerant electron theory of ferromagnetism. Spectra taken with nearly grazing incidence p-polarized light, however, are not interpretable in terms of the direct transition model. The importance of electron refraction is noted, as is the value of interpolation calculations for interpreting ARP spectra.     

SEPARATION OF PHOTOINDUCED CHLOROPHYLL-a CATION AND p-TETRABROMOBENZOQUINONE ANION ELECTRON SPIN RESONANCE LINES AT 35 GHz IN FROZEN VESICLE SOLUTIONS

Abstract— The photoionization products of chlorophyll-a with p-tetrabromobenzoquinone as an electron scavenger in rapidly frozen phospholipid vesicles have been detected by electron spin resonance. The asymmetric line resulting from the overlap of the chlorophyll-fl cation radical and the scavenger anion radical at 9 GHz (X band) has been resolved into two symmetric lines with different g values at 35 GHz (Q band).